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SMPS

Power Supply

  • A power supply unit (or PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer.

  • Power supplies are mainly categorized as linear power supplies and switched mode power supplies.

Power Supply

SMPS

  • 70 - 95 % efficiency.

  • Complex in design.

  • Small and light in size.

  • Filtering required.

Linear Power Supply

  • 30 - 40 efficiency.

  • Simple in design.

  • Large and heavy in size.

  • Low noise.

  • In a linear power supply, the input voltage from AC mains is first stepped down using a transformer.Stepped down voltage is then rectified and filtered using a capacitor. This unregulated dc voltage across the capacitor is finally given to linear regulator which converters it into regulated DC voltage as shown in the following figure.

What is SMPS?

  • SMPS (Switch Mode Power Supply) is a device which provides power to an electrical load and involves some kind of switching action.

  • An SMPS converts the AC line power directly into a DC voltage without a transformer, and this raw DC voltage is then converted into a higher frequency AC signal, which is used in the regulator circuit to produce the desired voltage and current.

  • Modern personal computers universally use switched-mode power supplies. 

Input

AC(75V-380V)

PC

SMPS

Output

  • DC 24V

  • DC 48V

  • DC 110V

  • DC 220V

Function of SMPS

  • A basic isolated AC to DC switched-mode power supply consists of:​

  • Input rectifier and filter

  • Inverter consisting of switching devices such as MOSFETs

  • Transformer

  • Output rectifier and filter

  • Feedback and control circuit

Why SMPS

  • As Linear power supplies become very bulky with an increase in its current ratings. So, we needed something which will allow us to handle a large number of currents without taking a lot of space.

  • SMPS is the solution for that.

  • SMPS works on a very high frequency as compared to linear power supplies.

  • Overal size of an SMPS become small.

Advantages

  • In general, a switch-mode power supply is best suited for portable equipment.

  • The usage of a transformer at high frequency (>20 kHz) in SMPS instead of using it directly at 50/60Hz as in linear power supply drastically reduces the size of a transformer which in turn decreases weight and size of power supply.

  • This also makes the operation of SMPS possible with a wide range of input voltage.

Application

  • The power supply in PCs.

  • Machine tool industries. 

  • Security Systems (Closed circuit cameras).

  • Mobile phone chargers.

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